The invention relates to a magnetic structure in which single-walled magnetic domains can propagate. The structure comprises a monocrystalline nonmagnetic substrate having a surface bearing a layer of monocrystalline magnetic material consisting of a rare earth iron garnet having a partial substitution of Mn.sup.3+ ions in iron sites. The layer is grown in compression on the substrate surface with an easy axis of magnetization substantially perpendicular to the plane of the layer and a medium axis of magnetization in the plane of the layer. The substrate surface is substantially parallel to a (110) crystal plane.
For generating and propagating single-walled magnetic domains, in particular cylindrical domains ("bubbles"), it is generally known to use a magnetic garnet material having an intrinsic uniaxial anisotropy and/or an induced uniaxial anisotropy (induced by stress or growth). This property is used for the formation of bubble domains by ensuring that an easy axis of magnetization is substantially perpendicular to the plane of the layer of the rare earth-iron garnet material. The term "rare earth" is to be understood herein as being an element having an atomic number of 39 or from 57 to 71 inclusive.
It is known from the article "New Bubble Materials With High Peak Velocity" by D. J. Breed at al. (IEEE Transactions on Magnetics, Vol. MAG 13, No. 3, September 1977, pp. 1087-1091) that in order to increase the velocity at which bubble domains can be propagated in garnet layers, garnet layers having an orthorhombic anisotropy have to be made. Layers having an orthorhombic anisotropy have an easy axis of magnetization perpendicular to the plane of the layer and hard axes of magnetization having two different degrees of "hardness" in the plane of the layer. These hard axes are often referred to as the "medium" axis and the "difficult" axis. The resulting anisotropy in the plane of the layer proves to have the same velocity-increasing effect as the known application of an external magnetic field acting in the plane of the layer. Such a field is, however, unsuitable for a number of bubble domain applications.
The above-mentioned article relates to bubble domain layers having an orthorhombic anisotropy grown in compression on gadolinium-gallium-garnet (GGG) substrates. The layers comprise manganese in some of the iron sites so as to obtain the desired magneto-structure properties. The required degree of compression is obtained by means of the choice of the rare earth ions. Since a layer of yttrium-iron garnet fits exactly on GGG, in order to provide a layer under compression a rare earth ion should be used which is larger than yttrium. However, magnetic properties such as the temperature dependence of the magnetization, are determined by the magnetic ions which are present at the iron sites and at the rare earth sites. This means that an yttrium iron garnet layer under compression on a GGG substrate cannot be obtained with a magnetic rare earth ion larger than yttrium, for example, gadolinium or europium, without, for example, influencing the temperature dependence of the magnetization. If, on the other hand, the compression of an yttrium iron garnet layer on GGG is to be obtained by means of a substituting nonmagnetic rare earth ion larger than yttrium, only lanthanum is available. It has been found, however, that lanthanum and manganese influence each other's incorporation in the layer so that the magneto-strictive properties are affected. In neither of the two cases is it thus possible to independently adjust the compression of an yttrium iron garnet epilayer on a GGG substrate.
In addition, the use of the magnetic rare earth ions gadolinium and europium for this purpose adversely adverse influences on the bubble-domain mobility (damping) while the overall magnetization is reduced. This is unfavorable for layers in which submicron bubble domains have to be generated and propagated.